During production of semiconductor devices, liquid crystal display devices or the like, a plasma processing apparatus that executes a specific type of processing such as etching or film formation on a substrate, e.g., a semiconductor wafer or a glass substrate for use in liquid crystal display devices, or the like, by applying thereto plasma generated inside a processing chamber, the internal pressure of which has been lowered to a predetermined level, is utilized.
While there are various types of plasma processing apparatuses known in the related art, most of them are plane-parallel plasma processing apparatuses having a susceptor (lower electrode) also used as a stage on which the substrate is placed, disposed toward the bottom inside the processing chamber, and an upper electrode also used as a processing gas delivery unit, disposed toward the top inside the processing chamber, so as to face opposite the susceptor.
In such a plane-parallel plasma processing apparatus, a specific type of processing gas is delivered into the processing chamber while the processing chamber is evacuated, so as to create a processing gas atmosphere achieving a predetermined degree of vacuum inside the processing chamber. In this state, high-frequency power with individually selected specific frequencies is supplied to the susceptor and the upper electrode, thereby generating plasma with the processing gas in the space between the substrate and the upper electrode. The substrate is processed, e.g. etched, as the plasma thus generated is applied to the substrate.
The upper electrode in this type of plasma processing apparatus is disposed at a position at which it is directly exposed to the plasma. In addition, a significant quantity of heat is generated at the upper electrode to which the high-frequency power with a high-level output for purposes of plasma generation is applied. Thus, the temperature of the upper electrode is likely to rise to an undesirably high level as the high-frequency power is applied thereto. Furthermore, the upper electrode with a greater thermal capacity compared to the lower electrode does not assure as good a response to temperature adjustment as the lower electrode. Consequently, it is not easy to sustain the temperature of the upper electrode at the desired temperature setting with a high level of accuracy.
The technologies developed for the upper electrode temperature adjustment in the known art include the one whereby the upper electrode is cooled by forming inside the upper electrode a flow passage through which a heating medium, such as a coolant or brine with the temperature thereof adjusted to a predetermined level, is to flow and distributing the heating medium through this flow passage (see, for instance, Japanese Laid Open Patent Publication No. 2004-342704(Patent Reference Literature 1) and Japanese Laid Open Patent Publication No. 2006-269944(Patent Reference Literature 2)).
In the plane-parallel plasma processing apparatus described above, a predetermined level of DC current may be superimposed over the high-frequency power and thus applied to the upper electrode together with the high-frequency power in order to achieve precision control of the potential of the plasma generated inside the processing chamber, the plasma density uniformity within the plane of the substrate and the like during the substrate processing (see, for instance, Japanese Laid Open Patent Publication No. 2006-270017(Patent Reference Literature 3)).
Tests and the like conducted by the inventor of the present invention et al. have revealed that such an application of a DC voltage to the upper electrode, too, causes an undesirable increase in the temperature of the upper electrode accompanied by a significant adverse effect on the characteristics (e.g., the etching rate, the device shape and the like) of the elements being formed on the substrate.
Since the upper electrode temperature control methods in the related art, such as those disclosed in patent reference literatures 1 and 2, do not take into consideration the heat transferred into the upper electrode as a DC voltage is applied to the upper electrode, the undesirable rise in the temperature of the upper electrode cannot be sufficiently prevented by directly adopting the temperature control technologies in a plasma processing apparatus in which a DC voltage is applied to the upper electrode.